AGM vs Flooded House batteries

[tkeithlu]

Time to replace my house bank, which is six flooded size 27s.

Previous threads have recommended the Duramax from Sams.

Flooded size 31, 105x20 AH, $80 each.
Flooded size 27, 90x20 AH, $62 each.
AGM size 27, 90x20 AH, $139 each.

Which is the best buy? Are AGMs that much of an advantage, basically twice or more length of life or number of charges? Is the extra capacity in the size 31 worth $19 more per battery?

Thanks. Those are questions above my pay grade.

[rslifkin]

If your setup works well with flooded, they're cheaper over their lifetime than AGM. Personally, I use AGMs for a couple of reasons: no need to top them off with water, reduced ventilation requirements, and less voltage sag under load. That means better performance when momentarily pulling a bunch of power (relative to the size of the bank) and also more flexibility in where they can be mounted.

As far as battery sizes and performance, if you can fit 6V golf cart batteries in a series/parallel setup they tend to hold up better in deep cycle applications than the 12v sizes often sold as "dual purpose" batteries.

Personally, my current house bank is a pair of the taller L16 6 volt batteries in series, making for 400ah at 12v. Your current 540ah would be pretty close to what you'd get from 4x 260AH GC2 6 volts in series/parallel. If you could fit 6 of them (or 4 of the taller L16s) you'd get 780AH (or 800AH with the L16s).

Gels are also an option if your charging setup can handle their slightly more fussy voltage requirements. Even in the standard 12v sizes they tend to handle deep cycling very well, and the good quality East Penn manufactured gels are available at every West Marine under their house brand "SeaGel".

[tkeithlu]

Thank you for a very informative answer. I've just measured, and golf cart batteries would lift the floor of the forward cabin, but then, this $62 (on sale at Sam's) looks like the best choice.

[NYSail]

Also has to do with your charging..... if you can’t top off your agms then you will shorten their life. Flooded are more forgiving..... so I have read.

[ranger58sb]

Originally Posted by tkeithlu

Time to replace my house bank, which is six flooded size 27s.

Previous threads have recommended the Duramax from Sams.

Flooded size 31, 105x20 AH, $80 each.
Flooded size 27, 90x20 AH, $62 each.
AGM size 27, 90x20 AH, $139 each.

Which is the best buy? Are AGMs that much of an advantage, basically twice or more length of life or number of charges? Is the extra capacity in the size 31 worth $19 more per battery?

105 Ah is about 16% more than 90 Ah. 630 Ah total gives you about 315 Ah usable (to 50% DoD), whereas 540 Ah total gives you about 270 Ah usable, also about a 16% increase. If your daily DC budget is large, more is better. If your budget is modest, maybe less is OK.

I prefer AGMs for our situation, but mostly for maintenance (none) and off-gassing (none) issues. Some also use AGMs for non-traditional mounting situations.

Happens we've gotten very good longevity from Odyssey AGMs; the verdict is still out on our more recent Lifeline AGMs. You'll notice both of those are hugely more expensive than the Sam's examples.

Anyway, I don't think AGMs, by definition, give you more cycles or longer life. Some do, some don't.

Compare the manufacturer's projected life cycle curve (usually to 50% DoD) to comparable flooded G31 and G29 batteries... and then compare same to Odyssey or Lifeline AGM G31 batteries (for Lifeline, look at their "deep cycle" version, not the starting battery)... and then compare same to flooded golf cart (GC2) batteries... and then to Lifeline's AGM golf cart batteries (GPL-4CTs).

IIRC, Odyssey and Lifeline both project about 1000 cycles to 50% DoD... and I think Trojan also predicts about 1000 cycles for their T-105 flooded GC2s.

Then you can do the subsequent math to arrive at $$ per Ah.

AGM GC2s mounted sideways might fit in places where normal upright mounting wouldn't have enough headroom.

-Chris

[Pete7]

This is a useful read every time I think about AGM batteries.

https://marinehowto.com/how-fast-can...ry-be-charged/

I guess if you need to run something with a high load like an induction hob or washing machine, AGMs could be useful to reduce the voltage sag. Also they seem to accept a higher charge current, good if you are charging with a genny.

We have neither so stick with FLA.

Pete

[Stu Jackson]

AGM Batteries - Making The Choice (from Maine Sail)

https://forums.sailboatowners.com/in...choice.124973/

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
https://forums.sailboatowners.com/in...teries.133773/

Additional Observations on the Limits of AGMs http://c34.org/bbs/index.php/topic,5....html#msg63004

[a64pilot]

Disregarding the Firefly as it’s an AGM, but as a general statement the lifespan for AGM’s and flooded seem to be very similar if you get quality batteries, but seem to cost about three times as much. In my opinion there are only a couple of quality AGM’s and your not getting them at Sam’s club, Costco etc..

So it depends on if the extra cost is worth not having to add water, can’t lay then on their side etc.

Firefly costs a little over 5 times as much per AH as a good quality Sams club flooded, but if you can believe the hype has a much greater usable capacity so that brings the cost back down to maybe 3 or 4 times as much, and you don’t have to fully recharge them, so that cuts way down on running some kind of motor to charge them, and again if you believe the hype the L15 size lasts seemingly pretty much forever.

I really, really want to believe they are as good as they say, cause if they are, to me they give me 99% of the advantages I have use for of an LFP bank, at much less cost, and way less complexity.

[smac999]

27's and 31's are for starting engines. not for house banks or cycling. (unless you get fireflys...)

try to fit some golf carts instead

personally I would never run flooded acid batt's in a boat simply because they are disgusting.

[ranger58sb]

Originally Posted by smac999

27's and 31's are for starting engines. not for house banks or cycling. (unless you get fireflys...)

There are at least one and a half other (AGM) exceptions. One if Lifeline's deep cycle G31 -- not their starting G31 -- and the half is Odyssey 31M-PC2150. Latter is certainly for starting engines, but they also spec a boatload of cycles similar to deep cycle specs.

-Chris

[MJH]

Originally Posted by tkeithlu

Time to replace my house bank, which is six flooded size 27s.

Previous threads have recommended the Duramax from Sams.

Flooded size 31, 105x20 AH, $80 each.
Flooded size 27, 90x20 AH, $62 each.
AGM size 27, 90x20 AH, $139 each.

Which is the best buy? Are AGMs that much of an advantage, basically twice or more length of life or number of charges? Is the extra capacity in the size 31 worth $19 more per battery?

Thanks. Those are questions above my pay grade.

There is more to the economics of electrical systems and battery group selection than cost.

Are all your batteries of the same chemistry? Do you have an external regulator and are the settings correct for the battery chemistry? Does your dock side battery charger allow for battery chemistry selection...is it properly set? Do you have temperature sensors on your battery banks and alternator? Are your batteries located in a living area or near an ignition source? Are you a put-them-in and forget-them type of sailor or are you meticulous in doing the maintenance required of the battery chemistry you purchase to maximize their life? Is your electrical systems total Ah's sufficient for your cruising style?

My first couple of boats were small and simple and I didn't concern myself with most of the above. Graduating to my present boat with broader dreams was a rude awakening to everything I didn't know about electrical systems...and I'm still learning.

Think about your goals; what kind of a total electrical system do you need to get you there? Then select the battery chemistry and group sizes you need and are willing to maintain.

Good Luck.

~ ~ _/) ~ ~ MJH

[tkeithlu]

Thanks again. Now I have lots to read and think about.

Since it was asked, all nine batteries in the boat are flooded and (at present) Interstate size 27s. Seven are charged by two routes. Shore power or either of two gensets power a ProMar 60 amp marine charger, set for them, or from the main engine via a Balmar alternator and electronic voltage regulator, ditto. The Balmar particularly had to be adjusted for a rather long fill time.

The other two are charged by very unsophisticated Delco single wire alternators on the main engine and the main genset.

Everything can be cross-wired, so I can start the main engine with the house bank, for example.

[belizesailor]

Consider your usage patterns and charging capacity. AGMs do not do well under repeated PSOC operation. If you cant bring them to full charge often then you will likely shorten their lifespan...thus negating any hypothetical advantages.

Lots of cruisers murder AGMs this way.

[tkeithlu]

I'm going to stick with flooded, but I'm curious. What is "PSOC" operation.

Thankfully, my system will bring the whole bank to full charge in a few hours. That's one advantage of a power boat.

[Bill O]

Now that you decided to stay w/FLAs, go for the golf cart 6V batteries.


A great bang for the buck and will last longer.


We are on yr. 8 w/ours and will probably go for at least another year before we change them. We have several Crown 235AH for our house bank (940AH) and each have slightly more capacity than the Trojan. If you have the height would get the slightly higher capacity.